Voltage regulator circuits can serve numerous purposes in integrated circuit devices. One particular application can be as a regulated internal power supply voltage for certain sections of an integrated circuit device. Even more particularly, voltage regulators can supply a power supply voltage to memory cell arrays within memory devices, such as dynamic random access memories (DRAMs) and static RAMs (SRAMs), as but two of the many possible applications.
Among the various types of voltage regulators are replica biased voltage regulators. Generally, in a replica biased voltage regulator a voltage established in one portion of a circuit (e.g., one leg), is replicated, typically by larger sized devices, to present a load (output) voltage. The load voltage is regulated by having it track the replica voltage as close as possible.
Prior art replica biased voltage regulators basically use active (dynamic) line regulation and passive (static) load regulation. Such approaches can achieve a good high-frequency transient response at the expense of poor DC load regulation.
In order to improve on DC load regulation and to prevent overshoots, either permanent or switched dummy loads have been proposed. Thus, existing replica biased voltage regulators have active (dynamic) line regulation and passive (static) load regulation. Various improvements have been proposed in order to better control output voltage over the load current range. These involve the use of fast voltage comparators in order to switch on/off dummy loads or additional current sourcing elements.
One example of an approach employing a switched dummy load is shown in FIG. 11. FIG. 11 shows a conventional replica biased voltage regulator circuit in a schematic diagram designated by the general reference character 1100.
In the example of FIG. 11, a voltage regulator circuit 1100 can include a dummy load (Rdummy), which can be switched into the output path when an output voltage (Vpwr) exceeds a reference voltage (Vref). Conversely, dummy load (Rdummy) can be isolated from an output when the output voltage (Vpwr) falls below the reference voltage (Vref). In this way, switched dummy load (Rdummy) can regulate output voltage (Vpwr) to a particular range.
Alternatively, in order to prevent Vpwr from dropping under increased current load conditions, the inclusion of switched P-type devices have been proposed, as presented in FIG. 12 and U.S. Pat. No. 6,373,231, issued to Lacey et al. on Apr. 16, 2002.
In the example of FIG. 12, a voltage regulator circuit 1200 can include p-type switching device P1 in addition to a permanent dummy load Rdummy. When an output voltage (Vpwr) exceeds a reference voltage (Vref), p-type device P1 can be turned off reducing current supplied to load device (Vdummy) and thus lowering output voltage. Conversely, when the output voltage (Vpwr) falls below the reference voltage (Vref), p-type device P1 can be turned on, increasing current supplied to load device (Vdummy) and thus raising the output voltage (Vpwr). In this way, a switched current supply can regulate output voltage (Vpwr) to a particular range.
The above conventional arrangements can suffer from drawbacks. First, active load regulation (e.g., switching in of load device, or switching on of current supplies) is not a proportional response or timewise continuous. This means that regulation only happens during periods of time when the load current is either extremely low or extremely high, as opposed to load regulation taking place at all times. Since voltage comparators (Comp) are used, the regulation provided can be considered a “winner takes all” type of regulation, as opposed to having proportionality between load current variation and compensation current.
Second, conventional switching load regulation can have an undesirable lag in response. Even if fast comparators are used, current technologies cannot guarantee response times faster than 1–2 nanoseconds. This may be insufficient in certain applications (e.g., fast SRAMs). That is, this load regulation mechanism can work poorly in the high frequency domain (10 MHz–1 GHz), since even fast voltage comparator driven feedback loops still have a response time on the order of a few nanoseconds.
Third, the above arrangement requires deploying extra voltage comparators. This can increase operating current consumption.
In light of the above, it would be desirable to arrive at a voltage regulator that does not suffer from the above drawbacks of conventional approaches.
More particularly, it would be desirable to provide a replica biased voltage regulator having active (dynamic) load regulation and reduced output impedance in both the low and high frequency domains.